Efforts to develop artificial blood pumps have spanned approximately ten years, including research both in the area of heart assist devices and total heart replacement units. One prominent design involves a polyeurathane bladder enclosed in a rigid metal alloy housing. Pneumatic pulses applied between the bladder and the housing produce a pumping action through the bladder, in conjunction with check valves at the bladder inlet and outlet ports. Imposition of the pulse expels the contents of the bladder and termination of the pulse permits the bladder to refill. In a left ventricular assist device, the bladder inlet would be connected to the left ventrical. The ventricular pressure plus resiliancy in the bladder, if any, causes the bladder to refill. Thus the strength of the heart and the rate at which the pneumatic system is depressurized between successive pulses determine the rate at which the bladder is filled.
The inside surface of the bladder is flocked with fibers of a blood-compatible polymeric material which promote the formation of a stable biological layer along the surface of the bladder. To preserve this layer and to otherwise minimize blood damage, the inside surfaces of the bladder should not be permitted to contact each other during operation.
Accordingly, it is an object of this invention to provide a control device for controlling the collapse pattern of the flexible bladder in a pneumatic blood pump.
Another object of this invention is to promote rapid filling of the bladder during depressurization of the pneumatic system.